White light LEDs (“WLEDs”) are increasingly used as backlight source in liquid crystal displays (“LCDs”) instead of cold cathode fluorescent lamps (“CCFLs”). A plurality of WLEDs may be connected in series to form a WLED string. Conventionally, circuitry for driving WLEDs may control a plurality of WLED strings synchronously. Such circuitry may comprise a voltage converter configured to provide a direct current (“DC”) driving voltage for each WLED string and a current balance circuit configured to regulate a current flowing through each WLED string.
The voltage converter (e.g., a PWM control circuit) and the current balance circuit may be integrated in a WLED application-specific integrated circuit (“ASIC”) chip. For example, FIG. 1 illustrates conventional circuitry for driving 2n WLED strings. The parameter “n” hereinafter is a random positive integer. As shown in FIG. 1, the conventional circuitry comprises two operation-up circuits 101-1 and 101-2 and two ASIC chips 102-1 and 102-2. Each of the operation-up circuits 101-1 and 101-2 provides a DC driving voltage Vdc to n WLED strings. Each of the ASIC chips 102-1 and 102-2 controls one of the corresponding operation-up circuits and regulates a current flowing through the corresponding n WLED strings.
If the circuitry shown in FIG. 1 needs to drive 3n WLED strings, an additional voltage converter and ASIC chip are required for the additional LED string. Thus, the conventional circuitry is inconvenient to expand to control additional WLED strings. Also, the conventional circuitry requires a large number of components with corresponding high costs and low efficiencies. Accordingly, certain improvements of circuitry for driving LED strings may be desirable.